This invention relates to a hot-air heater, especially for vehicles, having: a burner disposed in a housing and being fed with free-flowing fuel and, via a combustion-air fan, with combustion air; combustion-air, exhaust-gas and heating-air ducts constructed within said housing; and at least one space which, by means of a housing cover, can be closed off to the outside, said space being connected to at least one of the combustion-air and exhaust-gas ducts.
Heaters of this type are known, for example, from U.S. Pat. Nos. 3,989,029 and 3,989,030. After the housing cover is removed, the heater parts, such as a glow plug, a flame monitor or an adjustable throttling member, become accessible for an adjustment of the output of the combustion-air fan. The housing cover provides a tight closure in order to prevent exhaust-gas and/or combustion-air from escaping to the outside of the heater (except for exhaust-gas leaving via the exhaust pipe), so that it will not be conveyed, either directly or together with the heating-air conveyed, to the passenger area. This is especially important in the case of heaters intended for mounting inside of a vehicle. In this connection, the above-mentioned characteristic that the space that can be closed off to the outside by means of the cover is connected with the combustion-air and/or the exhaust-gas duct, must be understood in the widest sense. It must especially, also, apply to the situation where the mentioned space is normally closed off with respect to the combustion-air and exhaust-gas ducts, but exhaust-gas can penetrate into this space through leakages, for example, in the area of the glow plug thread.
In practice, there is the danger that a housing cover, that has been removed for maintenance or repair purposes, is, by mistake, not placed back on the housing. The exhaust-gas can then reach the passenger area (when the heater is used for vehicles) or another area that is to be heated and where people may be present and can be poisoned.
The invention, therefore, has a principle object of creating a hot-air heater of the initially-mentioned type where, in a simple and reliable manner, the possibility of people being injured, when the housing cover is erroneously not placed back on the housing, is avoided.
According to preferred embodiments of the invention, this object is achieved by the fact that, on the pressure side of the combustion-air fan, a combustion-air exhaust opening is provided which is blocked only when the cover is closed and is dimensioned in such a way that, when the combustion-air exhaust opening is not blocked, operation of the heater is not possible.
If, in the case of the hot-air heater according to the invention, the housing cover erroneously is not placed back on the housing after a maintenance or repair operation, so much combustion-air is let out that the heater cannot be operated and no exhaust-gases are produced containing toxic substances.
In accordance with further aspects of the invention, the combustion-air exhaust opening may be blocked by a part of the cover itself. A component that is used for fastening of the cover may also be used for the blocking of the exhaust opening, instead of the cover part.
As an additional safety measure, the combustion-air exhaust opening may have a cross section that is not circular. This would prevent that, when the cover is lost, for example, the heater is operated by closing the exhaust opening by means of a commercially available stopper or similar means.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.